1. Field of the Invention
The present invention relates to an ink jet recording apparatus, and particularly to a procedural structure for keeping an ink ejection performance in a good condition.
2. Description of the Related Art
In recent years, personal computers and office automation machines like word processors have been widely used, and a recording apparatus has also widely used as one way to output the processing results obtained by these apparatuses. A wire dotting method, a thermal printing method and an ink jet recording method are will known as a recording method used in the recording apparatus.
The ink jet recording method has several advantages that various kinds of recorded medium such as an unprocessed natural paper and a transparent sheet for OHP can be used and that the noise level generated during the recording operation is relatively small. One of ink fluid ejection methods used in the recording head of the ink jet recording method is to eject ink fluid by the pressure wave accompanied by the growth and diminish of a bubble in the ink fluid which is generated by the thermal energy. Recording heads using this ejection method are often formed within the following architecture. (1) Forming a plurality of heat-generation elements for generating thermal energy and driving circuits for driving heat-generation elements to generate thermal energy on a substrate made of silicon materials and so on in a similar fabricating processing to the semiconductor element processing. (2) By bonding the above defined substrate and a top plate having channels, forming a plurality of ink passages, each corresponding to each orifice and used for a chamber where thermal energy is transmitted to the ink fluid, a plurality of orifices, each defined at the open end part of each ink passage and used for ejecting ink fluid, and a common fluid reservoir defined at the opposite side to the orifice defined side of each ink passage and used for reserving ink fluid to supply ink fluid to each of the ink passages.
In addition to advantages obtained by the ink jet recording method, it will be appreciated that images recorded on the recording medium by using this type of recording head can be made to be clearer and finer because the structure of the orifice can be formed to be highly fine and precise. Additionally, the size of the recording head itself can be taken to be small and the fabricating and material cost can be reduced. So far, in recent years, the recording head ejecting ink fluid by using thermal energy as described above has been widely used in various kinds of recording apparatuses.
In case of such a recording head as the above described recording head having a relatively fine orifice and ink passage, an effect of the viscosity of the ink fluid on the ejection performance of the recording head is relatively high. For example, if the ink fluid in the ink passage near the orifice gets to be more viscous due to the evaporation of the solvent component of the ink fluid, there may be a case that the more viscous ink fluids disturb the ink fluid flow when ejecting ink fluid which leads to ink ejection failure such as the deflection of ejected ink fluid and the reduction of the amount of the ejected ink fluid and even results in the loss of ejecting ink fluid. And furthermore, in case that unnecessary ink droplets and unfavorable substances like paper powder adhere onto the orifice-disposed face of the recording head, the deflection of ejected ink fluid may occur and therefore the quality of recorded images may be reduced. As in the ink jet recording method, the ink fluid is ejected from the recording head onto the recording medium such as a paper sheet and a transparent sheet, for example, the ink mist composed of fine sized ink droplets may occur and the excess amount of the ink fluid ejected may rebound from the recording medium. As shown in FIG. 1, the ink mist and the rebounding ink fluid attach to the orifice-disposed face 1 of the recording head, and if the attaching ink fluid centers too much around the orifices 12, the ejection operation may be disturbed and the discharge direction may be deviated, and even the discharge operation may be stopped. In addition condensed water drops may be adhere onto the orifice-disposed face 1 due to the temperature difference between the recording head and the atmospheric air, which leads to the same adverse effects as found in case that the ink fluid attaches to the recording head.
With respect to the above described ink ejection failures due to increases in the viscosity of the ink fluid and the ink fluid drops adhere onto the orifice-disposed face, various kinds of operations for preventing these failures and for removing the causes to these failures in order to establish good-conditioned ink ejection operations are known as ejection restoration operations.
As one of these ejection restoration operations which is directed to resolve the ejection failure mainly due to increases in the viscosity of the ink fluids, for example, recognized is a capping operation in which a designated cap covers up the face on which the orifice of the recording head is formed (the orifice disposed face) in order to prevent water in the ink fluid from being evaporated from the orifice. A suction restoration operation is recognized, in which the viscous ink fluids are removed outside the recording head by sucking the ink fluid from the orifice by applying suction pressure inside the cap covering up the recording head. In addition, a pressurizing restoration operation is recognized as a substitution for the suction restoration operation or a combination with the suction restoration operation, in which the ink fluid is pressurized from the ink supply side of the ink passage and discharged from the orifice. In addition, as another ejection restoration operation, an ejection operation is recognized, in which the viscous ink fluid in the recording head is discharged by ejecting ink fluids not used for recording information or images on the recording media, and which is designated as an idle ejection operation. The above described ejection restoration operations are not only for removing the viscous ink fluids but also for removing bubbles in the ink fluid giving adverse effects on the ink fluid ejection performance.
As one of the ejection restoration operations which is directed to resolve the ejection failure mainly due to unfavorable substances adhering onto the recording head, a structure is known in which the orifice-disposed face is maintained to be cleaned in order to prevent the ejection direction deviation. In a typical structure, a wiping member is disposed so that the wiping member contacts the orifice-disposed face and is moved relatively to the face. As a result, the ink fluid droplets on the orifice-disposed face can be wiped off.
Unfavorable substances such as unnecessary ink fluids that adhere onto the orifice-disposed face are formed by ink mist generated in ejecting ink fluid and the ink fluid rebounding from the recording sheet in the recording operations of the recording head, and paper powder may be supposed to be adhesive onto the recording head when the recording head and paper sheets move relatively to each other in the recording operation.
Even in the ink jet recording apparatus performing the above described various kinds of ejection restoration operations, if the recording head has not been used for ejecting ink fluids for a long period of time, a certain amount of water in the ink fluid may be inevitably evaporated, and the ink fluids may get more viscous. In this case, at the start of recording operations after a long period during which the recording head has not been used, the recording head may bring about an ink ejection failure. So far, in the conventional ink jet recording apparatus, in order to prevent these ink ejection failures described above, it is required that the suction operation be performed at the start of the recording operation, that predetermined restoration procedures are performed in response to the viscosity of the ink fluid, and that ejection restoration operations are required for 5 to 30 seconds before the recording operation can be allowed to start.
The ink ejection failure caused by the viscous ink fluid filled in the recording head which has not been used for the recording operations for so long a period between several days and one year can be resolved only by a single suction restoration operation, and after this operation, the recording head can be used for the recording operation for several days to one week without restoration operations such as a suction operation which require a relatively long time before restarting the recording operation. However, in the case that natural paper sheet is used as a recording medium, prompt drying ink fluids are often used for fixing the ink fluid onto the recording medium and the recording operation is often performed in high temperature and low humidity. In such a case, even by the capping operation with the cap over the recording head, the ink fluid in the recording head is rapidly dried out and the viscosity of the ink fluid may increase in a relatively short period of time. So far, it is required to perform the idle ejection before and during the recording operation in order to prevent the ink ejection failure. In addition, in such an environment, if the period during which the recording head has not been used is so long, the viscous ink fluid cannot be completely removed only by the idle ejection operation.
With respect to the above mentioned problems in the viscous ink fluid, in the conventional ink jet recording apparatus, sealing of the recording head by the cap is fixed more firmly and materials through which the least amount of liquid or vapor penetrate are used for the cap. However, even though these conventional caps are used, the viscous ink fluids cannot be completely prevented, and hence, such a designated ejection restoration operation as a suction operation and so on is required prior to the recording operation.
In case of using a cap having highly hermetical sealing performances, the following problem occurs especially in the portable-type recording apparatus.
1. As the recording head is covered by the cap, due to the pressure variation in the cap caused by vibration and shocks during transportation, the meniscus formed in the ink passage near the orifice falls down inside the ink passage which leads to loss of the ink fluids in the ink passage and may cause the ink ejection failure.
2. Due to the atmospheric temperature change and the recording head temperature change, the air inside the cap may expand or contract, and therefore, there is still a problem that the meniscus falls down inside the ink ink passage and the ink fluid may be leaked out of the orifices by the suction, respectively.
With respect to the above described problem caused by the pressure variation, the ink jet recording apparatus having a cap halfway opened to the atmospheric air, a restoration system and a waste ink tank is proposed to enable to resolve this problem as a patent application by the assignee of the present invention. However, even in this apparatus, the above mentioned problem on the viscous ink fluids cannot be fully prevented.
In addition, as for the reliability of the restoration operations, in case that the gap is formed between the cap and the recording head due to paper powder and dust adhesive onto the cap and the orifice-disposed face of the recording head as described above, the evaporation of the solvent component of the ink fluid is activated further, and as a result, it is supposed that the ink ejection failure may easily occur.
On the other hand, in the ejection restoration operation using the above wiping structure, there are such substances which may remain on the orifice-disposed face such as the ink fluid and paper powders which are not wiped off by the blade. In the case that the ink fluids and so on remain adhered onto the orifice, liquid components of the ink fluid are evaporated and the ink fluid gets more viscous and paper powders adhere to the orifice-disposed face, and therefore, after a long period of time, the solidified ink fluid and paper powders cannot be removed even in the wiping operation with a blade. In the case that the ink fluid contains coloring materials and solvents which have such properties as getting more viscous or crystallization, a phenomena is found that the viscous ink fluid is piled up near the orifice as the evaporation of liquid components in the ink fluid proceeds and that the orifice is covered by the solidified ink fluid, which may lead to ink eject ion failures.
The viscous ink fluid remaining on the orifice-disposed face and the solidified ink fluid piled up near the orifice cannot removed only by the ordinary wiping operation with the blade and the idle ink fluid ejection operation. Prior to the idle ejection operation, even by heating the ink fluid up to an optimum temperature used for the recording operation of the recording head, ink ejection failures may often occur, and hence, in such a case, the viscous ink fluid remaining near the orifice is forced to be evacuated in many of the prior art apparatus. However, in such a case of restoring by the forced evacuation of the ink fluid as a suction operation, some problems are found to be unsolved with respect to scaling-up of the storage means like a waste ink tank in response to the evacuated amount of the ink fluid and reduction of the effective amount of the ink fluid to be used for the recording operation.